Targeted Degradation in Alzheimer Disease: Mechanisms, Clinical Insights, and Emerging Therapies

Abstract

Alzheimer disease (AD) remains a leading cause of dementia worldwide, characterized by progressive neurodegeneration and cognitive decline. Despite decades of research, disease-modifying treatments are limited. Recently, targeted protein degradation has emerged as a promising therapeutic strategy, offering the potential to directly modulate pathogenic proteins central to AD pathogenesis. This review discusses the epidemiology, pathophysiology, clinical presentation, diagnostic criteria, and traditional management of Alzheimer disease, with a focus on the latest advances in targeted degradation technologies. Mechanistic insights, clinical implications, and guideline recommendations are discussed to provide a comprehensive overview for clinicians and researchers.

Introduction

Alzheimer disease is a neurodegenerative disorder marked by progressive cognitive impairment, memory loss, and functional decline. As the most prevalent form of dementia, AD imposes a substantial burden on patients, families, and healthcare systems. Pathologically, it is characterized by extracellular amyloid-beta (Aβ) plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. Traditional therapies have focused on symptom management, but recent advances in targeted degradation are shifting the paradigm toward disease modification. This article reviews the landscape of AD with a focus on targeted degradation strategies, integrating recent evidence and practical clinical considerations.

Epidemiology / Disease Burden

Alzheimer disease affects over 55 million individuals globally, with projections estimating a near doubling by 2050 due to aging populations. It accounts for 60-80% of dementia cases and is a leading cause of disability and dependency among older adults. The economic burden is immense, with annual global costs exceeding $1 trillion. In clinical practice, AD is associated with increased morbidity, mortality, caregiver stress, and institutionalization rates. These data underscore the urgent need for effective, disease-modifying therapies.

Pathophysiology

The core pathophysiology of AD involves the accumulation of Aβ peptides, derived from amyloid precursor protein (APP) cleavage, and tau hyperphosphorylation leading to neurofibrillary tangles. These processes trigger synaptic dysfunction, neuroinflammation, oxidative stress, and neuronal loss. Importantly, the failure of cellular proteostasis and impaired clearance mechanisms contribute to the persistence of toxic protein aggregates. Targeted degradation approaches, such as proteolysis-targeting chimeras (PROTACs) and molecular glues, seek to harness the ubiquitin-proteasome system or autophagy-lysosome pathway to selectively degrade these pathogenic proteins, offering a mechanistic rationale for their therapeutic potential.

Risk Factors

Major risk factors for AD include advanced age, genetic predisposition (notably APOE ε4 allele), family history, vascular risk factors (hypertension, diabetes, dyslipidemia), traumatic brain injury, and lifestyle factors such as physical inactivity and poor diet. Recent studies suggest that impaired protein quality control and proteasome dysfunction may also constitute modifiable risk factors, linking them directly to the mechanistic underpinnings of targeted degradation strategies.

Clinical Features

Clinically, AD presents with insidious onset and gradual progression of memory impairment, particularly affecting recent episodic memory. As the disease advances, deficits in language, visuospatial abilities, executive function, and behavior emerge. Neuropsychiatric symptoms, such as depression, apathy, agitation, and psychosis, are common. The clinical course is characterized by progressive loss of independence and eventual need for full-time care.

Diagnosis

Diagnosis is based on clinical assessment, cognitive testing, and exclusion of other causes of dementia. Core criteria include evidence of progressive cognitive decline with impairment in one or more cognitive domains, interfering with daily function. Biomarker support via cerebrospinal fluid (CSF) assays (Aβ42, total tau, phosphorylated tau), structural and functional neuroimaging (MRI, FDG-PET, amyloid/tau PET), and genetic testing in select cases enhance diagnostic accuracy and allow for earlier detection. Recent guidelines emphasize the utility of biomarkers in both research and clinical settings.

Treatment & Management

Current management strategies focus on symptomatic relief and include cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and the NMDA receptor antagonist memantine. Non-pharmacological interventions—cognitive stimulation, physical activity, and caregiver support—are integral. However, these approaches do not alter disease progression. Disease-modifying therapies targeting Aβ (monoclonal antibodies such as aducanumab, lecanemab) have shown modest benefit and carry risks of amyloid-related imaging abnormalities (ARIAs). There remains an unmet need for therapies that address the underlying proteinopathies more effectively.

Recent Advances / Emerging Therapies

Targeted degradation technologies represent a paradigm shift in AD therapeutics. PROTACs are bifunctional molecules that recruit E3 ubiquitin ligases to specific target proteins, labeling them for proteasomal degradation. Preclinical studies have demonstrated selective degradation of tau and Aβ, resulting in reduced neurotoxicity and improved cognitive outcomes in animal models. Molecular glues and autophagy enhancers are also under investigation to facilitate degradation via distinct cellular pathways. Early-phase clinical trials are evaluating the safety, pharmacokinetics, and target engagement of these agents, with promising preliminary results. Challenges include delivery across the blood-brain barrier, off-target effects, and long-term safety. Nonetheless, targeted degradation holds promise for fundamentally altering the course of AD by removing the pathogenic drivers of neurodegeneration.

Guideline Recommendations

International guidelines currently endorse symptomatic management and recommend consideration of disease-modifying therapies in selected populations with early or prodromal AD and biomarker confirmation. The 2023 NIA-AA and EAN guidelines recognize the potential of novel therapeutics targeting proteinopathies, emphasizing the importance of biomarker-driven diagnosis and individualized treatment plans. As targeted degradation therapies progress through clinical trials, future guidelines will need to address their optimal use, patient selection, and monitoring strategies.

Conclusion

Targeted degradation is an emerging and highly promising therapeutic approach in Alzheimer disease, directly addressing the central proteinopathies implicated in its pathogenesis. While challenges remain, advances in molecular design and clinical translation offer hope for disease modification and improved patient outcomes. Ongoing research and guideline updates will be crucial to integrating these therapies into clinical practice and realizing their full potential in combating the global burden of Alzheimer disease.